The present invention relates to a combustion control system and method for a spark-ignition internal combustion engine.
A spark-ignition internal combustion engine is generally operated at a higher compression ratio for improvement in thermal efficiency, but such a performance improvement can be affected by engine knock.
Hence, a knock control system that monitors the occurrence of engine knock with a knock sensor and performs feedback control on ignition timing has been proposed and already come into use so as to prevent engine knock while maximizing engine thermal efficiency.
It is herein conceivable that the engine knock could be prevented more assuredly by not only carrying out a knock avoidance operation upon detection of the engine knock but also predicting knock occurrence according to a simulation model.
Further, the ignition timing is commonly set using a prescribed ignition-timing map with reference to engine speed and power and then adjusted on detection of the engine knock. A multiplicity of actual vehicle experiments must be conducted to prepare the ignition-timing map, and the number of experiments required to prepare the ignition-timing map becomes increased with the recent application of variable mechanisms including a variable valve mechanism and an exhaust gas recirculation mechanism. This results in higher cost and greater facility for engine development. It can be however expected that the prediction of knock occurrence by a simulation model will allow an omission of many or at least some of the experiments for preparation of the ignition-timing map to thereby provide a great advantage in engine development.
In view of the foregoing, Japanese Laid-Open Patent Publication No. 7-332149 proposes a combustion control device for an internal combustion engine, capable of predicting the autoignition timing of an unburned air-fuel mixture, or equivalently, the occurrence of engine knock and controlling combustion so as to avoid the engine knock in accordance with the prediction.